Sizing makes the native fiber network hydrophobic and thus prevents or reduces the penetration of water or other aqueous liquids into the paper. Sizing prevents the spreading and strike through of ink or printing colors. Papermaking fibers have a strong tendency to interact with water. This property is important for the development of strong interfiber hydrogen bonds, especially during drying, and is also the reason why paper loses its strength when rewetted. A high absorbency is important for certain paper grades such as toweling and tissue. Also corrugated medium paper must be able to absorb to a certain degree to convert properly in the corrugating process. On the other hand such properties are disadvantageous for many paper grades, e.g., liquid packaging, top layer of corrugated board, writing and printing papers, and most specialty papers. The water and liquid absorbency can be reduced by the addition of sizing agents to the paper stock and/or by their application to the paper surface.
Since the 1950s various forms of rosin size in the form of paste, dispersed, fortified formulations, alkyl ketene dimer (AKD) size, alkenyl succinic anhydride (ASA) size, and polymers mainly based on styrene acrylate and styrene maleinate sometimes called polymeric sizing agents (PSAs), have come onto the market. Today, beside starch for paper strength improvement and polymer binders for paper coating, sizing agents are the most important quality-improving additives in the paper manufacturing.
When applied in papermaking an emulsion or a dispersion of the sizing agent is prepared. Among other uses in papermaking, cationized starch is commonly used also as a stabilizing agent of the sizing agent emulsions or dispersions.
Pure starch is a white, tasteless and odorless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and helical amylose:
and the branched amylopectin:

Depending on the plant origin of starch, it generally contains from 20% to 25% amylose and from 75% to 80% amylopectin by weight.
Galactomannans are polysaccharides consisting of a mannose backbone with galactose side groups. A segment of galactomannan showing mannose backbone with a branching galactose unit on the top is illustrated below.

Non-ionic galactomannans such as guar gum have been used in emulsions of ASA sizing agent under controlled conditions. These ASA-guar gum emulsions were subjected to various treatments using a deposition rotor. Typically, the more guar gum is used in the emulsion, the more stable is the emulsion. The use of a further surfactant results in even less deposition, and a smaller average particle size of the emulsion.
In U.S. Pat. No. 4,606,773 an emulsion of alkenyl succinic anhydride (ASA) type of paper sizing agent is prepared using a cationic water-soluble polymer and a cationic starch as emulsifiers. In the disclosed method a water-soluble polymer is used as an emulsification aid. A cationically modified polymer having a molecular weight ranging between 20,000-750,000 is used in conjunction with water-soluble cationic starch, wherein the cationic starch to polymer weight ratio is between 75:25 to 25:75.
WO2008/145828 A1 discloses a xylan ester which may be present in a sizing composition. The esters are produced by reacting xylan with a short chained aliphatic carboxylic acid, such as formic, acetic, priopionic or butyric acid.
In the application of cationized starch for ASA stabilization typically a ratio from 1:1 to 4:1 of starch to ASA is used. Furthermore, starch used is also an important source of nutrition. Therefore, to develop more sustainable solutions for the future it would be highly advantageous to develop and use sizing agents comprising non-food based chemicals as emulsifiers in papermaking.